Lime mortar pointing is an integral part of the structure of
older properties. Porous brick and stone needs to breath to avoid becoming waterlogged,
lime mortar being less dense allows it to do so. Cement repointing can be incredibly
damaging to brick and stone work originally set with lime mortar, as where lime
mortar allows moisture to pass through it, cement mortar does not. Water and
moisture must then pass through the stone or brickwork instead which can cause
spalling, cracks in bricks, damp and rotten bricks and visible internal damp.

Traditional building construction is based on the use of
relatively soft and porous materials such as stone, brick, timber and cob,
together with a lime based mortar for bedding and plastering. These buildings
usually have solid walls, with no cavity, and are often built on insubstantial
foundations. They are therefore liable to settlement and movement associated
with seasonal changes in the ground conditions. Lime mortar is softer and
weaker than the stone or brick which it bonds and is therefore able to accommodate
slight movements caused by settlement or temperatures without significant
cracking. Also, it is permeable and allows evaporation of rising and
penetrating damp from within the wall. It is this permeability, or ‘breathing’,
which helps to keep the building dry inside without the damp proof course of
chemical treatments.

Solid Masonry walls, where solid, must have their pointing
maintained with lime mortar. It’s composition allows the transmission of water
and water vapour into and out of the building.

Conservation lime mortar repairs to old or listed buildings require
a considered approach. Lime mortar can be mixed to different levels of porosity
and strength, depending on the requirements of building. The original mortar
may be defective or ill-suited to the current condition of the house and its
surroundings, so it is important to gauge whether a different mix should be
used.

There should always be a competent inspection of the current
pointing work to establish and differentiate original mortar pointing and later
repairs. Unsuitable re-pointing should be raked out if possible (cement can be
very difficult to remove) and sound, original mortar should be left in place.

White concrete or dyes can be used by some contractors to
imitate lime mortar. Unfortunately unless you are familiar with the correct
texture, appearance and colouring of lime mortar, you may not know concrete has
been used until you notice the symptoms. Spalling, accelerated decay most noticeable
at the stone/mortar interface is one of the more common and most destructive issues
caused.

Pointing is vital in keeping a masonry wall weather-tight
and if done badly the results can be disastrous both technically and visually.
Pointing is intended to be sacrificial so that it decays in preference to the
stone or brick.